1. Field of the Invention
The present invention generally relates to heatsinks for cooling power electronic devices, especially devices used to provide power to an induction motor in an HVAC system. More particularly, this invention relates to a heatsink whereby cooling fluid comes in direct contact with the device to be cooled via a system of channels and wells over which the device is mounted.
2. Background of the Invention
Power electronic devices such as insulated gate bipolar transistors (IGBTs) and silicon-controlled rectifiers (SCRs) are typically cooled by mounting the devices within a housing which is secured to a heatsink or xe2x80x9ccold platexe2x80x9d. Cold plates are typically formed from a material which is highly thermally conductive, such as aluminum or copper, enabling the cold plate to readily conduct heat generated by the devices away from the devices and to the environment. Generally, heat is conducted by the cold plate to a structure which is designed to transfer the heat to the surrounding air or a liquid via conduction and convection.
A disadvantage with prior art cold plates is that heat transfer from a power electronic device is diminished to some degree because the heat must travel through the base plate of the housing in which the device is enclosed and across the interface between the base plate and the cold plate, before it reaches the cold plate. Heat transfer across the base plate-cold plate interface is highly dependent on the intimacy of the mating surfaces, which in turn is dependent on the flatness of the mating surfaces and the contact pressure generated by the fastener which secures the device to the cold plate. As a result, localized hot spots can occur in the base plate and cold plate, and the power electronic device is subject to higher operating temperatures. To mitigate this effect, larger and thicker base plates are often utilized to better distribute the heat across the base plate-cold plate interface. Thicker cold plates may also be necessary to provide a greater heatsink mass, particularly where more than one power electronic device is mounted to a single cold plate. Unfortunately, the additional weight resulting from increased base plate and cold plate thicknesses is often undesirable, particularly for applications within the automotive and aerospace industries. In addition, thicker cold plates also increase the thermal resistance, thus elevating the operating temperature of the electronics.
Transfer of heat to a fluid flowing through the cold plate is also known. Again, a thermally conductive metal cold plate is typically used, but with one or more passages being formed within the cold plate. As before, heat is conducted from the devices and to the environment via a cooling fluid flowing through the passages. Though enhanced heat transfer is possible with fluid-cooled cold plates, such cold plates share the same disadvantage noted above with the more conventional prior art cold plates. Specifically, heat transfer from the power electronic device is diminished because heat must travel through the base plate of the device and across the interface between the base plate and the cold plate before it reaches the cold plate. Consequently, power electronic devices cooled by fluid-cooled cold plates are also subject to higher operating temperatures.
Other disadvantages of the current fluid cooled cold plates are their effectiveness in cooling and their difficulty to manufacture. Currently, these fluid cooled cold plates typically come in two varieties. The first utilizes channels cut out of a base plate into which tubing, usually copper tubing, is placed. A thermally conductive epoxy is then laid on top of the tubing to hold it in place and to provide a thermal interface between the tube and the base plate. Cooling fluid is then introduced into the tubing to take the heat away from the electronic component. Utilizing the copper tubing allows the plate itself to be manufactured from aluminum which allows for reduced weight and easier manufacturing, but the heat transfer from the liquid through the tubing, the epoxy and into the device itself is not optimal.
Another technique utilizes a base plate made of copper or other suitable material into which channels are drilled for the flow of the cooling liquid. This type of base plate also has several disadvantages. Because the fluid is flowing through the plate itself, the material, such as copper, is often heavy and results in a base plate of significant weight. In addition, the channels often must be drilled from the edge and require that the holes then be brazed so as to create a sealed inner chamber. Another disadvantage is that these holes often turn at straight 90 degree angles due to the difficulty, if not impossibility, of drilling curved corners. This type of channel results in diminished flow capabilities. In addition, similar to the base plate utilizing copper tubing, the cooling capability of the heatsink must be transferred through the base plate and then into the electronic device itself.
In accordance with the invention, a cold plate for cooling electronic components comprising a base having a top surface onto which at least one electronic component is to be placed; a cooling well formed in the top of the base and open at the top; a feed channel formed in the base for accepting a cooling fluid to be introduced to the cooling well; a drain channel formed in the base through which the cooling fluid is to be carried away from the cooling well; a cooling well inlet formed in the cooling well and in communication with the feed channel; and a cooling well outlet formed in the cooling well opposite the cooling well inlet and in communication with the drain channel; wherein the feed drain channel is sufficiently large relative to the size and flow characteristics of the well and cooling well inlets and outlets such that when the cooling fluid flows through the cooling device, the pressure drop across the feed channel is substantially less than the pressure drop across the well.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description, serve to explain the principles of the invention.